From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=100.103.45.18 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1792438426; b=e8xYptfnM8Q7Z3OSOuv/ho50ZuvPtZKZBjhAFg4TpbjFA/woqEmT/ewotpWjPtQfwJEl mxX480DbwQt2Tuy9+PP5NYJUDrBz9jpmC9MxTcQVj9zgnvbQFEmzknuId2iLmbJ0Jthk/ YnKf1Wj6zQQg7kNJB56bJiYuOU9vcWcibvC0o5dXRD2uE3syG2ro2RTnUt7h9xEf+TgAH +7ZJcJzbrisy2UCcNhEEtvLAnN+Jgtx8Mn05ax+6wW+fJXS7XMtVGH9IVvtXKJIunD/cH VJadFPt4M8muNAulo7tjMX7XTZKOZPC5OSt9c79AFlxF76vJBLwgco+1UBDDE9W2hEA== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1792438426; h=Received:DKIM-Signature:Received:Message-ID:User-Agent:Date:From:To: Cc:Subject:References:MIME-Version:Content-Type; bh=psCXjxhPEu/IOcKYYRZ7VQz6lj9QwLsGpkDlLv06GGk=; b=5jq6LzeFSsKJQEXBotkLzmq5+1Ap4V/q1pyGtPrka21a2vtU76UL2LBxEX2qPDPgjEr2 y4OAbfs8oVsaIj7gYWDNzU9UERBKISrAeNAvaZOzNTMeEWU1l+kw0RG+xPqk3qTNgVxSN +NquaWQ5j3TsN79zPs2R4WhTgt4qAHT7zYMJr+e7gX4JBYNlpiYdUFL1f9nH4xq5t8Frb kqQiLRXf7yvMExGI2IwwLTivkOjJ/s+N0LBfJfPyZtB2GcF8Nzb1ZgS/ibz+BhZDtquqj A67buV1IRA0DOlwvAngDnViPlz2IQ0TRRrC5ssBxZvp92IkQ4abOpaXNQ1/qzND+jEQ== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b="eLOboJ/L"; arc=none smtp.remote-ip=100.103.45.18 Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (prime256v1)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 4D3E2606A31C for ; Mon, 19 Oct 2026 19:33:46 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key, unprotected) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=eLOboJ/L Received: by smtp.kernel.org (Postfix) with ESMTPSA id 295471F000C7; Mon, 19 Oct 2026 19:33:46 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1792438426; bh=psCXjxhPEu/IOcKYYRZ7VQz6lj9QwLsGpkDlLv06GGk=; h=Date:From:To:Cc:Subject:References; b=eLOboJ/LYOfw9WSm8vLJF/XvfydDbbkdda5M0YpfCdCf2OzXq60xjbGtU69tmePmD St77TKQZuQA8wtasfIluv6cTlfGQEmqiiHmaRt8QfTDh0XuE1lOHtjgXlQrKrX4x/o SxVTFoPdEUT2Ug0Ccg1mbnrgPonjAvjk09pTKwjYbY5IXkevla1u8MXnUJ5lDXlboM te1aUx/KRIi+LehnoqmKoynmBkxus/kRQR0EFFteHJBJWMKgzGn3UQmUXrCdZg6pDh IuuO1X24ormuTgu/IIEcMTiL1l/Ipv/uBPIW06afvfl3iDfPC9sYkCPN3sKGJ/Si7l haRVSipNOZZXg== Received: from rostedt by gandalf with local (Exim 4.100.1) (envelope-from ) id 1xIt7B-00000001ef8-20ey; Mon, 19 Oct 2026 15:33:45 -0400 Message-ID: <20261019193345.285303044@kernel.org> User-Agent: quilt/0.69 Date: Mon, 19 Oct 2026 15:33:32 -0400 From: Steven Rostedt To: linux-kernel@vger.kernel.org Cc: Masami Hiramatsu , Mark Rutland , Mathieu Desnoyers , Andrew Morton , Vincent Donnefort Subject: [for-next][PATCH 2/5] ring-buffer: Unify ring buffer minimum page calculations References: <20261019193330.365764549@kernel.org> X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 From: Vincent Donnefort The codebase scatters hardcoded minimum page limits across multiple places. Introduce RING_BUFFER_MIN_NR_PAGES and rb_calculate_nr_pages() to formalize the requirement of two pages in a ring buffer. Link: https://patch.msgid.link/20260911193937.602202-4-vdonnefort@google.com Signed-off-by: Vincent Donnefort Signed-off-by: Steven Rostedt --- include/linux/ring_buffer.h | 9 ++++++++- kernel/trace/ring_buffer.c | 32 +++++++++++++------------------ kernel/trace/simple_ring_buffer.c | 4 ++-- 3 files changed, 23 insertions(+), 22 deletions(-) diff --git a/include/linux/ring_buffer.h b/include/linux/ring_buffer.h index eac3e9080c3c..e4370064273e 100644 --- a/include/linux/ring_buffer.h +++ b/include/linux/ring_buffer.h @@ -98,6 +98,13 @@ struct trace_buffer *__ring_buffer_alloc_range(unsigned long size, unsigned flag void *ring_buffer_meta_scratch(struct trace_buffer *buffer, unsigned int *size); +/* + * A minimum of 2 pages ensures we can always swap a page out of the ring + * buffer. This does not account for the reader page or any other page + * containing meta data used by static ring buffers. + */ +#define RING_BUFFER_MIN_NR_PAGES 2UL + /* * Because the ring buffer is generic, if other users of the ring buffer get * traced by ftrace, it can produce lockdep warnings. We need to keep each @@ -287,7 +294,7 @@ static inline struct ring_buffer_desc *__first_ring_buffer_desc(struct trace_buf static inline unsigned long __calc_nr_pages_ring_buffer_desc(size_t size) { /* Takes into account the reader page */ - return max(DIV_ROUND_UP(size, PAGE_SIZE - BUF_PAGE_HDR_SIZE), 2UL) + 1; + return max(DIV_ROUND_UP(size, PAGE_SIZE - BUF_PAGE_HDR_SIZE), RING_BUFFER_MIN_NR_PAGES) + 1; } static inline size_t trace_buffer_desc_size(size_t buffer_size, unsigned int nr_cpus) diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c index 04bb94c29f58..1b148cd891c8 100644 --- a/kernel/trace/ring_buffer.c +++ b/kernel/trace/ring_buffer.c @@ -642,6 +642,11 @@ static __always_inline unsigned int rb_subbuf_max_data_size(struct trace_buffer return rb_subbuf_capacity(buffer) - RB_EVNT_HDR_SIZE - sizeof(event->array[0]); } +static unsigned long rb_calculate_nr_pages(struct trace_buffer *buffer, unsigned long size) +{ + return max(DIV_ROUND_UP(size, rb_subbuf_capacity(buffer)), RING_BUFFER_MIN_NR_PAGES); +} + /** * rb_subbuf_start - Get the start address of a subbuffer * @buffer: A trace buffer @@ -2864,7 +2869,7 @@ static struct trace_buffer *alloc_buffer(unsigned long size, unsigned flags, goto fail_free_buffers; /* Need at least two pages plus the reader page */ - if (nr_pages < 3) + if (nr_pages < RING_BUFFER_MIN_NR_PAGES + 1) goto fail_free_buffers; again: @@ -2876,7 +2881,7 @@ static struct trace_buffer *alloc_buffer(unsigned long size, unsigned flags, ptr += subbuf_size * nr_pages; } if (ptr > end) { - if (nr_pages <= 3) + if (nr_pages <= RING_BUFFER_MIN_NR_PAGES + 1) goto fail_free_buffers; nr_pages--; goto again; @@ -2899,13 +2904,10 @@ static struct trace_buffer *alloc_buffer(unsigned long size, unsigned flags, if (nr_pages > rb_static_max_pages()) goto fail_free_buffers; - if (nr_pages < 2) + if (nr_pages < RING_BUFFER_MIN_NR_PAGES) goto fail_free_buffers; } else { - /* need at least two pages */ - nr_pages = DIV_ROUND_UP(size, rb_subbuf_capacity(buffer)); - if (nr_pages < 2) - nr_pages = 2; + nr_pages = rb_calculate_nr_pages(buffer, size); } cpumask_set_cpu(cpu, buffer->cpumask); @@ -3318,11 +3320,7 @@ int ring_buffer_resize(struct trace_buffer *buffer, unsigned long size, mutex_lock(&buffer->mutex); atomic_inc(&buffer->resizing); - nr_pages = DIV_ROUND_UP(size, rb_subbuf_capacity(buffer)); - - /* we need a minimum of two pages */ - if (nr_pages < 2) - nr_pages = 2; + nr_pages = rb_calculate_nr_pages(buffer, size); if (cpu_id == RING_BUFFER_ALL_CPUS) { /* @@ -7502,12 +7500,8 @@ int ring_buffer_subbuf_order_set(struct trace_buffer *buffer, int order) } /* Update the number of pages to match the new size */ - nr_pages = old_capacity * buffer->buffers[cpu]->nr_pages; - nr_pages = DIV_ROUND_UP(nr_pages, rb_subbuf_capacity(buffer)); - - /* we need a minimum of two pages */ - if (nr_pages < 2) - nr_pages = 2; + nr_pages = rb_calculate_nr_pages(buffer, + old_capacity * buffer->buffers[cpu]->nr_pages); cpu_buffer->nr_pages_to_update = nr_pages; @@ -8102,7 +8096,7 @@ int trace_rb_cpu_prepare(unsigned int cpu, struct hlist_node *node) } /* allocate minimum pages, user can later expand it */ if (!nr_pages_same) - nr_pages = 2; + nr_pages = RING_BUFFER_MIN_NR_PAGES; buffer->buffers[cpu] = rb_allocate_cpu_buffer(buffer, nr_pages, cpu); if (!buffer->buffers[cpu]) { diff --git a/kernel/trace/simple_ring_buffer.c b/kernel/trace/simple_ring_buffer.c index 49913bb0057a..abfaf9bee12e 100644 --- a/kernel/trace/simple_ring_buffer.c +++ b/kernel/trace/simple_ring_buffer.c @@ -383,8 +383,8 @@ int simple_ring_buffer_init_mm(struct simple_rb_per_cpu *cpu_buffer, void *page; int i; - /* At least 1 reader page and two pages in the ring-buffer */ - if (desc->nr_page_va < 3) + /* At least RING_BUFFER_MIN_NR_PAGES and 1 reader page */ + if (desc->nr_page_va < RING_BUFFER_MIN_NR_PAGES + 1) return -EINVAL; memset(cpu_buffer, 0, sizeof(*cpu_buffer)); -- 2.53.0